A known electronic engine control system comprises a processor-based engine controller that processes data from various sources to develop control data for controlling certain functions of the engine, including fueling of the engine by injection of fuel into engine combustion chambers. Control of engine fueling involves several factors. One is the quantity of fuel injected during an injection. Another is the timing of an injection. Consequently, the control system must set both the quantity of fuel injected and the time at which the injection occurs during an engine operating cycle.
A known diesel engine that powers a motor vehicle has an oil pump that delivers oil under pressure to an oil rail serving electric-actuated fuel injection devices, or simply fuel injectors, that use oil from the oil rail to force injections of fuel. The pressure in the oil rail is sometimes referred to as injector control pressure, or ICP, and that pressure is under the control of an appropriate ICP control strategy that is an element of the overall engine control strategy implemented in the engine control system. ICP is a factor in setting the quantity of fuel injected during an injection.
Examples of fuel systems containing fuel injection devices that utilize ICP oil to force fuel into engine combustion chambers via plungers are found in U.S. Pat. Nos. 5,460,329; 5,597,118; 5,722,373; and 6,029,628. The device of the latter has a plunger that is displaced within a pumping chamber by oil at ICP from an oil rail to force fuel out of an internal pumping chamber of the device. The ICP oil pressure amplifies the fuel pressure within the device to a magnitude large enough for forcing a normally closed control valve at an outlet of the device to open. When that outlet control valve opens, the amplified fuel pressure forces fuel through the outlet and into the corresponding combustion chamber.
Because ICP in the oil rail is a significant factor in setting the quantity of fuel injected during an injection, the ability to accurately control ICP is of obvious importance in an engine control strategy. Control of ICP is of course complicated because changing engine conditions can act in ways that tend to change ICP.
Changes in desired ICP that result from the processing of certain data by a processor of the engine controller to set desired ICP are one source of complication. Another source is how a particular oil system responds to changing conditions. Consequently, closed-loop control of ICP is one strategy for securing the best correspondence of actual ICP to desired ICP.
Because control of fuel injection impacts tailpipe emissions, improvements in control of fuel injection can reduce the amount of undesired products of combustion in tailpipe emissions. Where laws and regulations concerning tailpipe emissions are becoming increasingly strict, an ability to achieve reduced tailpipe emissions is seen to be vitally important to engine and motor vehicle manufacturers.